Inside Bitcoin

1//===- FuzzedDataProvider.h - Utility header for fuzz targets ---*- C++ -* ===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8// A single header library providing an utility class to break up an array of
9// bytes. Whenever run on the same input, provides the same output, as long as
10// its methods are called in the same order, with the same arguments.
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
14#define LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
15
16#include <algorithm>
17#include <array>
18#include <climits>
19#include <cstddef>
20#include <cstdint>
21#include <cstdlib>
22#include <cstring>
23#include <initializer_list>
24#include <limits>
25#include <string>
26#include <type_traits>
27#include <utility>
28#include <vector>
29
30// In addition to the comments below, the API is also briefly documented at
31// https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#fuzzed-data-provider
32class FuzzedDataProvider {
33 public:
34  // |data| is an array of length |size| that the FuzzedDataProvider wraps to
35  // provide more granular access. |data| must outlive the FuzzedDataProvider.
36  FuzzedDataProvider(const uint8_t *data, size_t size)
37      : data_ptr_(data), remaining_bytes_(size) {}
38  ~FuzzedDataProvider() = default;
39
40  // See the implementation below (after the class definition) for more verbose
41  // comments for each of the methods.
42
43  // Methods returning std::vector of bytes. These are the most popular choice
44  // when splitting fuzzing input into pieces, as every piece is put into a
45  // separate buffer (i.e. ASan would catch any under-/overflow) and the memory
46  // will be released automatically.
47  template <typename T> std::vector<T> ConsumeBytes(size_t num_bytes);
48  template <typename T>
49  std::vector<T> ConsumeBytesWithTerminator(size_t num_bytes, T terminator = 0);
50  template <typename T> std::vector<T> ConsumeRemainingBytes();
51
52  // Methods returning strings. Use only when you need a std::string or a null
53  // terminated C-string. Otherwise, prefer the methods returning std::vector.
54  std::string ConsumeBytesAsString(size_t num_bytes);
55  std::string ConsumeRandomLengthString(size_t max_length);
56  std::string ConsumeRandomLengthString();
57  std::string ConsumeRemainingBytesAsString();
58
59  // Methods returning integer values.
60  template <typename T> T ConsumeIntegral();
61  template <typename T> T ConsumeIntegralInRange(T min, T max);
62
63  // Methods returning floating point values.
64  template <typename T> T ConsumeFloatingPoint();
65  template <typename T> T ConsumeFloatingPointInRange(T min, T max);
66
67  // 0 <= return value <= 1.
68  template <typename T> T ConsumeProbability();
69
70  bool ConsumeBool();
71
72  // Returns a value chosen from the given enum.
73  template <typename T> T ConsumeEnum();
74
75  // Returns a value from the given array.
76  template <typename T, size_t size> T PickValueInArray(const T (&array)[size]);
77  template <typename T, size_t size>
78  T PickValueInArray(const std::array<T, size> &array);
79  template <typename T> T PickValueInArray(std::initializer_list<const T> list);
80
81  // Writes data to the given destination and returns number of bytes written.
82  size_t ConsumeData(void *destination, size_t num_bytes);
83
84  // Reports the remaining bytes available for fuzzed input.
85  size_t remaining_bytes() { return remaining_bytes_; }
86
87 private:
88  FuzzedDataProvider(const FuzzedDataProvider &) = delete;
89  FuzzedDataProvider &operator=(const FuzzedDataProvider &) = delete;
90
91  void CopyAndAdvance(void *destination, size_t num_bytes);
92
93  void Advance(size_t num_bytes);
94
95  template <typename T>
96  std::vector<T> ConsumeBytes(size_t size, size_t num_bytes);
97
98  template <typename TS, typename TU> TS ConvertUnsignedToSigned(TU value);
99
100  const uint8_t *data_ptr_;
101  size_t remaining_bytes_;
102};
103
104// Returns a std::vector containing |num_bytes| of input data. If fewer than
105// |num_bytes| of data remain, returns a shorter std::vector containing all
106// of the data that's left. Can be used with any byte sized type, such as
107// char, unsigned char, uint8_t, etc.
108template <typename T>
109std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t num_bytes) {
110  num_bytes = std::min(num_bytes, remaining_bytes_);
111  return ConsumeBytes<T>(num_bytes, num_bytes);
112}
113
114// Similar to |ConsumeBytes|, but also appends the terminator value at the end
115// of the resulting vector. Useful, when a mutable null-terminated C-string is
116// needed, for example. But that is a rare case. Better avoid it, if possible,
117// and prefer using |ConsumeBytes| or |ConsumeBytesAsString| methods.
118template <typename T>
119std::vector<T> FuzzedDataProvider::ConsumeBytesWithTerminator(size_t num_bytes,
120                                                              T terminator) {
121  num_bytes = std::min(num_bytes, remaining_bytes_);
122  std::vector<T> result = ConsumeBytes<T>(num_bytes + 1, num_bytes);
123  result.back() = terminator;
124  return result;
125}
126
127// Returns a std::vector containing all remaining bytes of the input data.
128template <typename T>
129std::vector<T> FuzzedDataProvider::ConsumeRemainingBytes() {
130  return ConsumeBytes<T>(remaining_bytes_);
131}
132
133// Returns a std::string containing |num_bytes| of input data. Using this and
134// |.c_str()| on the resulting string is the best way to get an immutable
135// null-terminated C string. If fewer than |num_bytes| of data remain, returns
136// a shorter std::string containing all of the data that's left.
137inline std::string FuzzedDataProvider::ConsumeBytesAsString(size_t num_bytes) {
138  static_assert(sizeof(std::string::value_type) == sizeof(uint8_t),
139                "ConsumeBytesAsString cannot convert the data to a string.");
140
141  num_bytes = std::min(num_bytes, remaining_bytes_);
142  std::string result(
143      reinterpret_cast<const std::string::value_type *>(data_ptr_), num_bytes);
144  Advance(num_bytes);
145  return result;
146}
147
148// Returns a std::string of length from 0 to |max_length|. When it runs out of
149// input data, returns what remains of the input. Designed to be more stable
150// with respect to a fuzzer inserting characters than just picking a random
151// length and then consuming that many bytes with |ConsumeBytes|.
152inline std::string
153FuzzedDataProvider::ConsumeRandomLengthString(size_t max_length) {
154  // Reads bytes from the start of |data_ptr_|. Maps "\\" to "\", and maps "\"
155  // followed by anything else to the end of the string. As a result of this
156  // logic, a fuzzer can insert characters into the string, and the string
157  // will be lengthened to include those new characters, resulting in a more
158  // stable fuzzer than picking the length of a string independently from
159  // picking its contents.
160  std::string result;
161
162  // Reserve the anticipated capacity to prevent several reallocations.
163  result.reserve(std::min(max_length, remaining_bytes_));
164  for (size_t i = 0; i < max_length && remaining_bytes_ != 0; ++i) {
165    char next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
166    Advance(1);
167    if (next == '\\' && remaining_bytes_ != 0) {
168      next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
169      Advance(1);
170      if (next != '\\')
171        break;
172    }
173    result += next;
174  }
175
176  result.shrink_to_fit();
177  return result;
178}
179
180// Returns a std::string of length from 0 to |remaining_bytes_|.
181inline std::string FuzzedDataProvider::ConsumeRandomLengthString() {
182  return ConsumeRandomLengthString(remaining_bytes_);
183}
184
185// Returns a std::string containing all remaining bytes of the input data.
186// Prefer using |ConsumeRemainingBytes| unless you actually need a std::string
187// object.
188inline std::string FuzzedDataProvider::ConsumeRemainingBytesAsString() {
189  return ConsumeBytesAsString(remaining_bytes_);
190}
191
192// Returns a number in the range [Type's min, Type's max]. The value might
193// not be uniformly distributed in the given range. If there's no input data
194// left, always returns |min|.
195template <typename T> T FuzzedDataProvider::ConsumeIntegral() {
196  return ConsumeIntegralInRange(std::numeric_limits<T>::min(),
197                                std::numeric_limits<T>::max());
198}
199
200// Returns a number in the range [min, max] by consuming bytes from the
201// input data. The value might not be uniformly distributed in the given
202// range. If there's no input data left, always returns |min|. |min| must
203// be less than or equal to |max|.
204template <typename T>
205T FuzzedDataProvider::ConsumeIntegralInRange(T min, T max) {
206  static_assert(std::is_integral_v<T>, "An integral type is required.");
207  static_assert(sizeof(T) <= sizeof(uint64_t), "Unsupported integral type.");
208
209  if (min > max)
210    abort();
211
212  // Use the biggest type possible to hold the range and the result.
213  uint64_t range = static_cast<uint64_t>(max) - static_cast<uint64_t>(min);
214  uint64_t result = 0;
215  size_t offset = 0;
216
217  while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
218         remaining_bytes_ != 0) {
219    // Pull bytes off the end of the seed data. Experimentally, this seems to
220    // allow the fuzzer to more easily explore the input space. This makes
221    // sense, since it works by modifying inputs that caused new code to run,
222    // and this data is often used to encode length of data read by
223    // |ConsumeBytes|. Separating out read lengths makes it easier modify the
224    // contents of the data that is actually read.
225    --remaining_bytes_;
226    result = (result << CHAR_BIT) | data_ptr_[remaining_bytes_];
227    offset += CHAR_BIT;
228  }
229
230  // Avoid division by 0, in case |range + 1| results in overflow.
231  if (range != std::numeric_limits<decltype(range)>::max())
232    result = result % (range + 1);
233
234  return static_cast<T>(static_cast<uint64_t>(min) + result);
235}
236
237// Returns a floating point value in the range [Type's lowest, Type's max] by
238// consuming bytes from the input data. If there's no input data left, always
239// returns approximately 0.
240template <typename T> T FuzzedDataProvider::ConsumeFloatingPoint() {
241  return ConsumeFloatingPointInRange<T>(std::numeric_limits<T>::lowest(),
242                                        std::numeric_limits<T>::max());
243}
244
245// Returns a floating point value in the given range by consuming bytes from
246// the input data. If there's no input data left, returns |min|. Note that
247// |min| must be less than or equal to |max|.
248template <typename T>
249T FuzzedDataProvider::ConsumeFloatingPointInRange(T min, T max) {
250  if (min > max)